(1) Term for a friend who often steals from others, hides things or is generally a shady individual and should not be trusted.
(2) Term for an individual strung out on excess use of narcotics. Their actions when put in front of the general public appear to be off, or sketchy.
"I let you guys borrow my sister's jewelry and now all of it is missing. Did you take any without putting it back?"
"No, but Sketcharella just left and she could barely carry her purse."
Someone who after doing copious amounts of cocaine becomes super paranoid and thinks that everyone is out to get them. Frequently happens to heavy users and retards. Sketchtardness is contagious and can be passed to others, thereby making it a buzzkill as well. If you see or are hanging out with a sketchtard slap them immediately, or distract them by doing karaoke to Vanilla Ice "Ice Ice baby..."
Tim: "Holy fuck is that a cop car?"
Jim: "No assfuck its a carola, stop being such a sketchtard and lets do another lizzle."